Choose your builder/dealer first. An architect may or may not know about some of the technical considerations of the modular concept. A particular modular manufacturer may have length limitations based on factory size, delivery equipment, transport laws, etc.. Start with a dealer.

I guess it all depends on how much you want to spend. Just about all modular companies have design staffs and can custom make a home.
Also what are your limitations? Slope? Lot size? drainage?

I am not recommending this company, but I have seen their products first hand up here in Vermont as there's a whole subdivision using theor product. But they can and do build custom houses to your specs.

Click the link below

Here is a link that might be useful: Westchester Modular

One of th emain things you want to do is find a manufacturing facility that's within 200 miles of your lot. There are many such places in the northeast. Going halfway across the country to find a manufacturer can be costly as far as transportation goes. Find a company that has a rep in NJ and start there. Also decide if you just want the home delivered and you'll do the general contracting or if you want the dealer to be the GC also. I had the dealer handle everything since I was in PA and the lot was in VT. And they did a very nice job.

If you are in northern NJ, I would agree that you should check out Westchester Modular Homes. Also check out Chelsea Modular Homes, which is only a short drive from Westchester Modular. They built their reputation on custom design services. (Full disclosure time: I was the CAD manager for Chelsea for a long time before moving north.) Tell them I recommended them.

Wayne